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ISSUE 3  May 17, 2001

 

CEREAL LEAF BEETLE ISSUES FOR 2001

Cereal leaf beetles (CLB) were found in Williams and McKenzie counties by state surveys in June, 2000. No reports of significant damage, treatments, or other needs to manage this insect in the field were reported. The insect is expanding its range eastward, following the Missouri River. Southwestern ND counties are also at some risk since the beetle has at least been detected in adjacent Montana counties. NDSU and the ND Department of Agriculture plan to continue surveys this year.

However, now that we know CLB is present, grain growers in these and neighboring counties should be vigilant for potential problems this year. This beetle feeds on the foliage of cereal grains (oats, wheat, barley, corn and rye; oats are the preferred host).

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The first sign of CLB activity in the spring is adult feeding damage on the plant foliage. While this is the first sign of adult activity, adults are not the target of control. Cereal leaf beetle adults are 3/16 inch long. The adult beetles are brightly colored, which aids in identification and detection. The first pair of wings (the elytra) are hard and are metallic blue-black. The legs of adults and the prothorax (first segment behind the head) are red. The brown larvae are often covered with black, shiny mucus. Fully grown larvae are 1/4 inch long.

The larvae feed on leaves by eating streaks of tissue from the upper surface of the leaf. Larvae-damaged leaves have long, narrow feeding strips between the veins. Eggs and larvae are monitored by plant inspection since thresholds are expressed as egg and larval numbers per plant or per stem. Examine 10 plants per location and select 1 location for every 10 acres of field. Count number of eggs and larvae per plant (small plants) or per stem (larger plants) and get an average number of eggs and larvae, based on the samples you have taken.

Plant growth stage should be noted because the treatment threshold changes with plant growth stage (3 eggs and larvae or more per plant in tillering smaller plants; 1 larvae per flag leaf at boot stage). Both eggs and larvae can be found by examining the upper leaf surface.

Economic Threshold

Boot stage is a critical point in plant development and impact of cereal leaf beetle feeding damage can be felt on both yield and grain quality. Before boot stage, the threshold is: 3 eggs and larvae or more per plant (including all the tillers present before the emergence of the flag leaf). Larvae feeding in early growth stages can have a general impact on plant vigor. When the flag leaf emerges, feeding is generally restricted to the flag leaf which can significantly impact grain yield and quality. The threshold is decreased at the boot stage to: 1 larvae or more per flag leaf.

Registered insecticides to control CLB in wheat, barley and oats are: malathion, and Lannate. In addition, these insecticides are registered for CLB in wheat only: Warrior and Sevin.

FLEA BEETLE INSECTICIDE COMPATIBLE WITH ROUNDUP USE IN RR CANOLA

It is that time of year that we should be monitoring seedling canola for flea beetle activity. Jan Knodel, Crop Protection Specialist, Minot, is reporting movement of flea beetles (see Around the State items). A common question that comes up at this time is the tank mix compatibility of Capture, a pyrethroid insecticide used to control flea beetles, with glyphosate (e.g., RoundUp).

There should be no problems with this mixture. Plot trials conducted by J. Knodel and Dr. B. Jenks in 1999 evaluated two different pyrethroids in combination with glyphosate (RoundUp Ultra). They observed no phytotoxic effects on plants. Weed control was not reduced. Control of flea beetles was the same between treatments. Monsanto has not reported any problems with these mixtures. Finally, there have not been any reports of problems from a number of people who used this mixture last year.

Phillip Glogoza, Extension Entomologist
pglogoza@ndsuext.nodak.edu


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